PROJECT ABSTRACT Hepatitis C is a major public health challenge particularly among HIV infected people who inject drugs (PWID). Despite recent availability of new oral, efficacious HCV therapies of short duration with minimal side effects, rates of HCV treatment in PWID remain low. Accelerated rates of liver disease progression in HIV/HCV co- infected individuals make HCV treatment among HIV infected PWID a priority. PWID social networks have the potential to serve as vehicles to increase rates of HCV treatment and prevent HCV reinfection. There is however little know about PWID social networks as it relates to HCV infection, care access and transmission patterns in inner city US populations. The goal of this project is to fill these knowledge gaps as a bridge to developing effective combined biomedical and behavioral (bio-behavioral) interventions to improve HCV treatment and prevent HCV reinfection among HIV infected PWID. I am an infectious disease trained physician with training in epidemiology, prior laboratory experience in molecular methods and practical clinical experience providing HIV and HCV care to inner-city HIV infected PWID. My long term goal is to conduct sophisticated clinical trials of combined biomedical and behavioral interventions to improve HCV/HIV medical care, treatment and prevention as well as understand transmission dynamics to prevent HCV reinfection. The proposed studies are nested in two NIDA funded PWID cohorts, the prevention and testing (Lighthouse) study and the AIDS Linked to the IntraVenous Experience (ALIVE) cohort, both representing HIV infected and uninfected inner-city Baltimore PWID. Aim 1 utilizes data from social networks of index HIV-infected PWID to determine if HCV clusters within PWID social networks. Aim 2 will assess individual- and network-level barriers and facilitators of HCV care among HIV infected PWID in the oral DAA era. Aim 3 will assess if social networks document HCV transmission through use of complementary social network and phylogenetic analyses. The proposed career development plan will expand my technical skills through additional expertise in: (1) social network analyses; (2) recruitment of PWID social networks and assessment of social determinants of PWID HCV/HIV related health outcomes; 3) phylogenetic analyses and 4) implementation of bio-behavioral interventions. I will be well supported within the Department of Medicine at Johns Hopkins University and will benefit from the excellent research infrastructure of the Lighthouse and ALIVE studies at Johns Hopkins. With the recent national epidemic of transition from oral opioid to injection drug use and attendant increase in HIV and HCV infection rates, development of sustainable interventions to increase rates of HCV treatment among PWID and reduce rates of HIV/HCV infection have become a priority. This award will facilitate my pathway to an independent career as a patient-oriented clinical investigator committed to developing interventions to increase rates of HCV treatment and prevent HCV reinfection among HIV infected PWID.